Method of manufacturing high resistivity semiconductor-on-insulator wafers with charge trapping layers

ABSTRACT

A method of preparing a single crystal semiconductor handle wafer in the manufacture of a semiconductor-on-insulator device is provided. The single crystal semiconductor handle wafer is prepared to comprise a charge trapping layer, which is oxidized. The buried oxide layer in the resulting semiconductor-on-insulator device comprises an oxidized portion of the charge trapping layer and an oxidized portion of the single crystal semiconductor device layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 15/526,798, filed May 15, 2017, the entire disclosure of which ishereby incorporated by reference in its entirety. U.S. application Ser.No. 15/526,798 is the U.S. national stage application of InternationalApplication No. PCT/US2015/060674, filed Nov. 13, 2015 and published asWO 2016/081313, the entire disclosure of which is hereby incorporated byreference in its entirety. International Application No.PCT/US2015/060674 claims priority to U.S. Provisional Patent ApplicationNo. 62/081,359 filed on 18 Nov. 2014, the entire disclosure of which ishereby incorporated by reference in its entirety.

THE FIELD OF THE INVENTION

The present invention generally relates to the field of semiconductorwafer manufacture. More specifically, the present invention relates to amethod of preparing a handle substrate for use in the manufacture of asemiconductor-on-insulator (e.g., silicon-on-insulator) structure, andmore particularly to a method for producing a charge trapping layer inthe handle wafer of the semiconductor-on-insulator structure.

BACKGROUND OF THE INVENTION

Semiconductor wafers are generally prepared from a single crystal ingot(e.g., a silicon ingot) which is trimmed and ground to have one or moreflats or notches for proper orientation of the wafer in subsequentprocedures. The ingot is then sliced into individual wafers. Whilereference will be made herein to semiconductor wafers constructed fromsilicon, other materials may be used to prepare semiconductor wafers,such as germanium, silicon carbide, silicon germanium, or galliumarsenide.

Semiconductor wafers (e.g., silicon wafers) may be utilized in thepreparation of composite layer structures. A composite layer structure(e.g., a semiconductor-on-insulator, and more specifically, asilicon-on-insulator (SOI) structure) generally comprises a handle waferor layer, a device layer, and an insulating (i.e., dielectric) film(typically an oxide layer) between the handle layer and the devicelayer. Generally, the device layer is between 0.01 and 20 micrometersthick, such as between 0.05 and 20 micrometers thick. In general,composite layer structures, such as silicon-on-insulator (SOI),silicon-on-sapphire (SOS), and silicon-on-quartz, are produced byplacing two wafers in intimate contact, followed by a thermal treatmentto strengthen the bond.

After thermal anneal, the bonded structure undergoes further processingto remove a substantial portion of the donor wafer to achieve layertransfer. For example, wafer thinning techniques, e.g., etching orgrinding, may be used, often referred to as back etch SOI (i.e., BESOI),wherein a silicon wafer is bound to the handle wafer and then slowlyetched away until only a thin layer of silicon on the handle waferremains. See, e.g., U.S. Pat. No. 5,189,500, the disclosure of which isincorporated herein by reference as if set forth in its entirety. Thismethod is time-consuming and costly, wastes one of the substrates, andgenerally does not have suitable thickness uniformity for layers thinnerthan a few microns.

Another common method of achieving layer transfer utilizes a hydrogenimplant followed by thermally induced layer splitting. Particles (e.g.,hydrogen atoms or a combination of hydrogen and helium atoms) areimplanted at a specified depth beneath the front surface of the donorwafer. The implanted particles form a cleave plane in the donor wafer atthe specified depth at which they were implanted. The surface of thedonor wafer is cleaned to remove organic compounds deposited on thewafer during the implantation process.

The front surface of the donor wafer is then bonded to a handle wafer toform a bonded wafer through a hydrophilic bonding process. Prior tobonding, the donor wafer and/or handle wafer are activated by exposingthe surfaces of the wafers to plasma containing, for example, oxygen ornitrogen. Exposure to the plasma modifies the structure of the surfacesin a process often referred to as surface activation, which activationprocess renders the surfaces of one or both of the donor water andhandle wafer hydrophilic. The wafers are then pressed together, and abond is formed there between. This bond is relatively weak, and must bestrengthened before further processing can occur.

In some processes, the hydrophilic bond between the donor wafer andhandle wafer (i.e., a bonded wafer) is strengthened by heating orannealing the bonded wafer pair. In some processes, wafer bonding mayoccur at low temperatures, such as between approximately 300° C. and500° C. In some processes, wafer bonding may occur at high temperatures,such as between approximately 800° C. and 1100° C. The elevatedtemperatures cause the formation of covalent bonds between the adjoiningsurfaces of the donor wafer and the handle wafer, thus solidifying thebond between the donor wafer and the handle wafer. Concurrently with theheating or annealing of the bonded wafer, the particles earlierimplanted in the donor wafer weaken the cleave plane.

A portion of the donor wafer is then separated (i.e., cleaved) along thecleave plane from the bonded wafer to form the SOI wafer. Cleaving maybe carried out by placing the bonded wafer in a fixture in whichmechanical force is applied perpendicular to the opposing sides of thebonded wafer in order to pull a portion of the donor wafer apart fromthe bonded wafer. According to some methods, suction cups are utilizedto apply the mechanical force. The separation of the portion of thedonor wafer is initiated by applying a mechanical wedge at the edge ofthe bonded wafer at the cleave plane in order to initiate propagation ofa crack along the cleave plane. The mechanical force applied by thesuction cups then pulls the portion of the donor wafer from the bondedwafer, thus forming an SOI wafer.

According to other methods, the bonded pair may instead be subjected toan elevated temperature over a period of time to separate the portion ofthe donor wafer from the bonded wafer. Exposure to the elevatedtemperature causes initiation and propagation of a crack along thecleave plane, thus separating a portion of the donor wafer. This methodallows for better uniformity of the transferred layer and allows recycleof the donor wafer, but typically requires heating the implanted andbonded pair to temperatures approaching 500° C.

The use of high resistivity semiconductor-on-insulator (e.g.,silicon-on-insulator) wafers for RF related devices such as antennaswitches offers benefits over traditional substrates in terms of costand integration. To reduce parasitic power loss and minimize harmonicdistortion inherent when using conductive substrates for high frequencyapplications it is necessary, but not sufficient, to use substratewafers with a high resistivity. Accordingly, the resistivity of thehandle wafer for an RF device is generally greater than about 500Ohm-cm. With reference now to FIG. 1, a silicon on insulator structure 2comprises a very high resistivity silicon wafer 4, a buried oxide (BOX)layer 6, and a silicon device layer 10. Such a substrate is prone toformation of high conductivity charge inversion or accumulation layers12 at the BOX/handle interface causing generation of free carriers(electrons or holes), which reduce the effective resistivity of thesubstrate and give rise to parasitic power losses and devicenonlinearity when the devices are operated at RF frequencies. Theseinversion/accumulation layers can be due to BOX fixed charge, oxidetrapped charge, interface trapped charge, and even DC bias applied tothe devices themselves.

A method is required therefore to trap the charge in any inducedinversion or accumulation layers so that the high resistivity of thesubstrate is maintained even in the very near surface region. It isknown that charge trapping layers (CTL) between the high resistivityhandle substrates and the buried oxide (BOX) may improve the performanceof RF devices fabricated using SOI wafers. A number of methods have beensuggested to form these high interface trap layers. For example, withreference now to FIG. 2, one of the method of creating asemiconductor-on-insulator 20 (e.g., a silicon-on-insulator, or SOI)with a CTL for RF device applications is based on depositing an undopedpolycrystalline silicon film 28 on a silicon substrate having highresistivity 22 and then forming a stack of oxide 24 and top siliconlayer 26 on it. A polycrystalline silicon layer 28 acts as a highdefectivity layer between the silicon substrate 22 and the buried oxidelayer 24. See FIG. 2, which depicts a polycrystalline silicon film foruse as a charge trapping layer 28 between a high resistivity substrate22 and the buried oxide layer 24 in a silicon-on-insulator structure 20.An alternative method is the implantation of heavy ions to create a nearsurface damage layer. Devices, such as radiofrequency devices, are builtin the top silicon layer 26.

It has been shown in academic studies that the polycrystalline siliconlayer in between of the oxide and substrate improves the deviceisolation, decreases transmission line losses and reduces harmonicdistortions. See, for example: H. S. Gamble, et al.“Low-loss CPW lineson surface stabilized high resistivity silicon,” Microwave Guided WaveLett., 9(10), pp. 395-397, 1999; D. Lederer, R. Lobet and J.-P. Raskin,“Enhanced high resistivity SOI wafers for RF applications,” IEEE Intl.SOI Conf., pp. 46-47, 2004; D. Lederer and J.-P. Raskin, “New substratepassivation method dedicated to high resistivity SOI wafer fabricationwith increased substrate resistivity,” IEEE Electron Device Letters,vol. 26, no. 11, pp.805-807, 2005; D. Lederer, B. Aspar, C. Laghaé andJ.-P. Raskin, “Performance of RF passive structures and SOI MOSFETstransferred on a passivated HR SOI substrate,” IEEE International SOIConference, pp. 29-30, 2006; and Daniel C. Kerret al. “Identification ofRF harmonic distortion on Si substrates and its reduction using atrap-rich layer”, Silicon Monolithic Integrated Circuits in RF Systems,2008. SiRF 2008 (IEEE Topical Meeting), pp. 151-154, 2008.

The properties of polycrystalline silicon charge trapping layer dependupon the thermal treatments the semiconductor-on-insulator (e.g.,silicon-on-insulator) receives. A problem that arises with these methodsis that the defect density in the layer and interface tend to anneal outand become less effective at charge trapping as the wafers are subjectedto the thermal processes required to make the wafers and build deviceson them. Accordingly, the effectiveness of polycrystalline silicon CTLdepends on the thermal treatments that SOI receives. In practice, thethermal budget of SOI fabrication and device processing is so high thatthe charge traps in conventional polycrystalline silicon are essentiallyeliminated. The charge trapping efficiency of these films becomes verypoor.

SUMMARY OF THE INVENTION

In one aspect, the objective of this invention is to provide a method ofmanufacturing semiconductor-on-insulator (e.g., silicon-on-insulator)wafers with thermally stable charge trapping layers, which preserve thecharge trapping effectiveness and significantly improve the performanceof completed RF devices.

Briefly, the present invention is directed to a multilayer structurecomprising: a single crystal semiconductor handle substrate comprisingtwo major, generally parallel surfaces, one of which is a front surfaceof the single crystal semiconductor handle substrate and the other ofwhich is a back surface of the single crystal semiconductor handlesubstrate, a circumferential edge joining the front and back surfaces ofthe single crystal semiconductor handle substrate, a bulk region betweenthe front and back surfaces, and a central plane of the single crystalsemiconductor handle substrate between the front and back surfaces ofthe single crystal semiconductor handle substrate, wherein the singlecrystal semiconductor handle substrate has a minimum bulk regionresistivity of 100 Ohm-cm; a charge trapping layer in interfacialcontact with the front surface layer of the single crystal siliconhandle substrate, the charge trapping layer comprising one or moresemiconductor layers, wherein each of the one or more semiconductorlayers comprise a polycrystalline structure or an amorphous structureand further wherein each of the one or more semiconductor layerscomprises a material selected from the group consisting of silicon,SiGe, SiC, and Ge; a semiconductor oxide layer in interfacial contactwith the charge trapping layer, the semiconductor oxide layer comprisinga first bonding surface; a dielectric layer, the dielectric layercomprising a second bonding surface, the second bonding surface of thedielectric layer in interfacial contact with the first bonding surfaceof the first semiconductor oxide layer; and a single crystalsemiconductor device layer in interfacial contact with the dielectriclayer.

The present invention is further directed to a method of preparing asemiconductor-on-insulator device. The method comprises: forming acharge trapping layer on a front surface layer of a single crystalsemiconductor handle substrate, wherein the single crystal semiconductorhandle substrate comprises two major, generally parallel surfaces, oneof which is the front surface of the single crystal semiconductor handlesubstrate and the other of which is a back surface of the single crystalsemiconductor handle substrate, a circumferential edge joining the frontand back surfaces of the single crystal semiconductor handle substrate,a bulk region between the front and back surfaces, and a central planeof the single crystal semiconductor handle substrate between the frontand back surfaces of the single crystal semiconductor handle substrate,wherein the single crystal semiconductor handle substrate has a minimumbulk region resistivity of 100 Ohm-cm and further wherein the chargetrapping layer comprises one or more semiconductor layers, wherein eachof the one or more semiconductor layers comprise a polycrystallinestructure or an amorphous structure and further wherein each of the oneor more semiconductor layers comprises a material selected from thegroup consisting of silicon, SiGe, SiC, and Ge; forming a semiconductoroxide layer on the charge trapping layer, wherein the semiconductoroxide layer has a thickness of at least about 0.1 micrometers; andbonding the semiconductor oxide layer to a dielectric layer on a frontsurface layer of a single crystal semiconductor donor substrate tothereby prepare a bonded structure, wherein the single crystalsemiconductor donor substrate comprises two major, generally parallelsurfaces, one of which is the front surface of the single crystalsemiconductor donor substrate and the other of which is a back surfaceof the single crystal semiconductor donor substrate, a circumferentialedge joining the front and back surfaces of the single crystalsemiconductor donor substrate, and a central plane of the single crystalsemiconductor donor substrate between the front and back surfaces of thesingle crystal semiconductor donor substrate, wherein the single crystalsemiconductor donor substrate comprises a cleave plane and thedielectric layer on the front surface layer of the single crystalsemiconductor donor substrate.

The present invention is still further directed to a method of preparinga silicon-on-insulator structure. The method comprises: bonding a firstbonding surface on a front surface layer of a single crystal siliconhandle substrate to a second bonding surface on a front surface layer ofa single crystal silicon donor substrate; wherein the single crystalsilicon handle substrate comprises two major, generally parallelsurfaces, one of which is the front surface of the single crystalsilicon handle substrate and the other of which is a back surface of thesingle crystal silicon handle substrate, a circumferential edge joiningthe front and back surfaces of the single crystal silicon handlesubstrate, a bulk region between the front and back surfaces, and acentral plane of the single crystal silicon handle substrate between thefront and back surfaces of the single crystal silicon handle substrate,wherein the single crystal silicon handle substrate has a minimum bulkregion resistivity of 100 Ohm-cm, and further wherein a charge trappinglayer is in interfacial contact with the front surface layer of thesingle crystal silicon handle substrate, the charge trapping layercomprising one or more semiconductor layers, wherein each of the one ormore semiconductor layers comprise a polycrystalline structure or anamorphous structure and further wherein each of the one or moresemiconductor layers comprises a material selected from the groupconsisting of silicon, SiGe, SiC, and Ge, and further wherein asemiconductor oxide layer is in interfacial contact with the chargetrapping layer, the semiconductor oxide layer comprising the firstbonding surface; and wherein the single crystal silicon donor substratecomprises two major, generally parallel surfaces, one of which is thefront surface of the single crystal silicon donor substrate and theother of which is a back surface of the single crystal silicon donorsubstrate, a circumferential edge joining the front and back surfaces ofthe single crystal silicon donor substrate, and a central plane of thesingle crystal silicon donor substrate between the front and backsurfaces of the single crystal silicon donor substrate, wherein thesingle crystal silicon donor substrate comprises a cleave plane and adielectric layer on the front surface layer of the single crystalsilicon donor substrate, the dielectric layer comprising the secondbonding surface.

Other objects and features of this invention will be in part apparentand in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a silicon-on-insulator wafer comprising a highresistivity substrate and a buried oxide layer.

FIG. 2 is a depiction of a silicon-on-insulator wafer according to theprior art, the SOI wafer comprising a polycrystalline silicon chargetrapping layer between a high resistivity substrate and a buried oxidelayer.

FIG. 3 is a depiction of a silicon-on-insulator wafer according to themethod of the present invention. The SOI wafer was prepared as describedin Example 1.

DETAILED DESCRIPTION OF THE EMBODIMENT(S) OF THE INVENTION

According to the present invention, a method is provided for producing acharge trapping layer on a single crystal semiconductor handlesubstrate, e.g., a single crystal semiconductor handle wafer, such as asingle crystal silicon handle wafer. The single crystal semiconductorhandle wafer comprising the charge trapping layer is useful in theproduction of a semiconductor-on-insulator (e.g., silicon-on-insulator)structure. According to the present invention, the charge trapping layerin the single crystal semiconductor handle wafer is formed at the regionnear the oxide interface. Advantageously, the method of the presentinvention provides a charge trapping layer that is stable againstthermal processing, such as subsequent thermal process steps in theproduction of the semiconductor-on-insulator substrate and devicemanufacture.

In some embodiments, the method of the present invention is directed toproducing a charge trapping layer at the handle/buried oxide (“BOX”)interface of a semiconductor-on-insulator (e.g., silicon-on-insulator)structure. According to the method of the present invention, a chargetrapping layer comprising one or more layers of a semiconductor materialsuch as silicon, SiGe, SiC, and Ge, which may be polycrystalline oramorphous, is deposited onto an exposed front surface of a singlecrystal semiconductor handle substrate, e.g., a wafer, having a highresistivity. The charge trapping layer comprising amorphous orpolycrystalline semiconductor material acts as a high density trapregion to kill the conductivity in the handle substrate at the interfacewith the BOX and prevent the formation of induced charge inversion oraccumulation layers that can contribute to power loss and non-linearbehavior in electronic devices designed for RF operation. According tothe present invention, the charge trapping layer is oxidized prior tobonding with a single crystal semiconductor donor substrate such thatthe polycrystalline or amorphous charge trapping layer (e.g., apolycrystalline or amorphous silicon charge trapping layer) comprises anoxide layer (a semiconductor oxide layer, e.g., a silicon dioxide layer)of a thickness greater than 0.1 micrometer. In some embodiments, thecharge trapping layer is oxidized prior to bonding with a single crystalsemiconductor donor substrate such that the polycrystalline or amorphouscharge trapping layer (e.g., a polycrystalline or amorphous siliconcharge trapping layer) comprises an oxide layer (a semiconductor oxidelayer, e.g., a silicon dioxide layer) of a thickness no greater thanabout 10 micrometers. Accordingly, the oxide layer (a semiconductoroxide layer, e.g., a silicon dioxide layer) in contact with thepolycrystalline or amorphous charge trapping layer (e.g., apolycrystalline or amorphous silicon charge trapping layer) may have athickness between about 0.1 micrometer and about 10 micrometers, such asbetween about 0.1 micrometers and about 4 micrometers, such as betweenabout 0.1 micrometers and about 2 micrometers, or between about 0.1micrometers and about 1 micrometer.

Advantageously, by forming a charge trapping layer comprising one ormore layers of semiconductor material such as silicon, SiGe, SiC, andGe, which may be polycrystalline or amorphous, on the front surface of ahigh resistivity single crystal semiconductor substrate and by oxidizingthe charge trapping layer to form a semiconductor oxide layer (e.g., asilicon dioxide layer, a germanium dioxide layer, a silicon germaniumdioxide layer) on the handle substrate comprising the charge trappinglayer, the charge trapping layer is more thermally stable to the hightemperature thermal budget of SOI fabrication compared to apolycrystalline silicon charge trapping layer that is not oxidized priorto bonding with a single crystal semiconductor donor substrate. Apolycrystalline silicon charge trapping layer, for example, may bethermally unstable to the high temperature thermal budget in that aportion of the individual polycrystalline silicon grains have a tendencyto dissolve at the high temperatures of semiconductor-on-insulator(e.g., silicon-on-insulator) fabrication (typically, up to or evenexceeding 1100° C.) while some polycrystalline silicon grains grow insize upon cooling until the grains grow in size toward or evenessentially matching the total thickness of charge trapping layer. Thetendency of polycrystalline silicon grains to grow during thermalprocessing of the semiconductor-on-insulator (e.g.,silicon-on-insulator) structure, which is observed starting attemperatures as low as 600° C., reduces the overall defectivity of thecharge trapping layer, which in turn reduces the charge trappingefficiency of the charge trapping layer.

According to the method of the present invention, deposition ofsemiconductor material such as silicon, SiGe, SiC, and Ge, which may bepolycrystalline or amorphous, to form the charge trapping layer isfollowed by oxidation in order to form an oxide layer (e.g., a silicondioxide layer, a germanium dioxide layer, a silicon germanium dioxidelayer) on the charge trapping layer on the single crystal semiconductorhandle substrate. The oxide layer (e.g., a silicon dioxide layer, agermanium dioxide layer, a silicon germanium dioxide layer) has beendetermined to cause oxygen atoms to poison or passivate the grainboundaries of the charge trapping layer semiconductor material prior. Bypoisoning the grain boundaries, the diffusion of silicon and/orgermanium atoms through grain boundaries is slowed, andrecrystallization is reduced. According to current understanding andresults to date, the poisoning of the grain boundaries by oxygen atomsimproves the thermal stability of the charge trapping layer and thusimproves the efficiency of the charge trapping layer. Accordingly, thefinal semiconductor-on-insulator structure retains a much higher overalllevel of defectivity compared to the prior art process in which a singlelayer of polycrystalline silicon comprises the entirety of the chargetrapping layer.

Oxidation of the charge trapping layer, e.g., a polycrystalline siliconlayer, prior to bonding with the single crystal semiconductor donorsubstrates may additionally enhance contamination control. In thisregard, background impurities may and often normally deposit on exposedsurfaces at uncontrolled level. High temperature processing in SOIstructure manufacturing may cause impurity diffusion that is accompaniedby polycrystalline silicon resistivity reduction and enhancedpolycrystalline silicon recrystallization. These factors may contributeto degraded performance of the charge trapping layer. In embodimentswherein the charge trapping layer is oxidized to form a semiconductoroxide film (e.g., a silicon dioxide layer, a germanium dioxide layer, asilicon germanium dioxide layer) on the charge trapping layer, thegrowing oxide accumulates many types of background impurities, such asBoron, and blocks other impurities from the diffusion into the chargetrapping layer, e.g., polycrystalline silicon charge trapping layer.Additionally, pre-bonding and bonding processes may contaminate thesurfaces of wafers. Forming a semiconductor oxide layer (e.g., a silicondioxide layer, a germanium dioxide layer, a silicon germanium dioxidelayer) film on the surface of the charge trapping layer comprising,e.g., polycrystalline silicon, seals all such contamination within theoxide and prevents the diffusion of contaminating impurities into thecharge trapping layer.

Still further, the method of the present invention may contribute tocontrol over bow of the semiconductor-on-insulator structure, e.g.,silicon-on-insulator. In this regard, due to the difference in thecoefficients of thermal expansion between silicon oxide and silicon, forexample, high intrinsic stresses develop in the oxide films on siliconwafers. In embodiments wherein the buried oxide film (i.e., the “BOX”)is contributed by oxide on the surface of the donor structure, the finalsemiconductor-on-insulator structure has oxide from one wafer only and,therefore, it is deformed by the oxide stresses. In embodiments of theinvention in which the buried oxide layer is contributed, at leastpartially, by the handle substrate, the oxide grown on the backside ofthe handle wafer balances the SOI wafer stress state and reduces its bowor warp.

Finally, it has been observed that post-processing of the chargetrapping layer, e.g., polycrystalline silicon, may be reduced in themethod of the present invention. In this regard, chemical mechanicalpolishing (“CMP”) may be omitted. In embodiments in which CMP isomitted, the interface between the buried oxide and the charge trappinglayer in the final structure is highly rough. The rough interfacebenefits by reducing polycrystalline silicon conductivity due to chargecarrier scattering at the rough interface. This improves RF deviceperformance.

The substrates for use in the present invention include a semiconductorhandle substrate, e.g., a single crystal semiconductor handle wafer anda semiconductor donor substrate, e.g., a single crystal semiconductordonor wafer. The semiconductor device layer in asemiconductor-on-insulator composite structure is derived from thesingle crystal semiconductor donor wafer. The semiconductor device layermay be transferred onto the semiconductor handle substrate by waferthinning techniques such as etching a semiconductor donor substrate orby cleaving a semiconductor donor substrate comprising a damage plane.In general, the single crystal semiconductor handle wafer and singlecrystal semiconductor donor wafer comprise two major, generally parallelsurfaces. One of the parallel surfaces is a front surface of thesubstrate, and the other parallel surface is a back surface of thesubstrate. The substrates comprise a circumferential edge joining thefront and back surfaces, a bulk region between the front and backsurfaces, and a central plane between the front and back surfaces. Thesubstrates additionally comprise an imaginary central axis perpendicularto the central plane and a radial length that extends from the centralaxis to the circumferential edge. In addition, because semiconductorsubstrates, e.g., silicon wafers, typically have some total thicknessvariation (TTV), warp, and bow, the midpoint between every point on thefront surface and every point on the back surface may not precisely fallwithin a plane. As a practical matter, however, the TTV, warp, and boware typically so slight that to a close approximation the midpoints canbe said to fall within an imaginary central plane which is approximatelyequidistant between the front and back surfaces.

Prior to any operation as described herein, the front surface and theback surface of the substrate may be substantially identical. A surfaceis referred to as a “front surface” or a “back surface” merely forconvenience and generally to distinguish the surface upon which theoperations of method of the present invention are performed. In thecontext of the present invention, a “front surface” of a single crystalsemiconductor handle substrate, e.g., a single crystal silicon handlewafer, refers to the major surface of the substrate that becomes aninterior surface of the bonded structure. It is upon this front surfacethat the charge trapping layer is formed. Accordingly, a “back surface”of a single crystal semiconductor handle substrate, e.g., a handlewafer, refers to the major surface that becomes an exterior surface ofthe bonded structure. Similarly, a “front surface” of a single crystalsemiconductor donor substrate, e.g., a single crystal silicon donorwafer, refers to the major surface of the single crystal semiconductordonor substrate that becomes an interior surface of the bondedstructure. The front surface of a single crystal semiconductor donorsubstrate often comprises a dielectric layer, e.g., a silicon dioxidelayer, which forms the buried oxide (BOX) layer in the final structure.A “back surface” of a single crystal semiconductor donor substrate,e.g., a single crystal silicon donor wafer, refers to the major surfacethat becomes an exterior surface of the bonded structure. Uponcompletion of conventional bonding and wafer thinning steps, the singlecrystal semiconductor donor substrate forms the semiconductor devicelayer of the semiconductor-on-insulator (e.g., silicon-on-insulator)composite structure.

The single crystal semiconductor handle substrate and the single crystalsemiconductor donor substrate may be single crystal semiconductorwafers. In preferred embodiments, the semiconductor wafers comprise asemiconductor material selected from the group consisting of silicon,silicon carbide, silicon germanium, gallium arsenide, gallium nitride,indium phosphide, indium gallium arsenide, germanium, and combinationsthereof. The single crystal semiconductor wafers, e.g., the singlecrystal silicon handle wafer and single crystal silicon donor wafer, ofthe present invention typically have a nominal diameter of at leastabout 150 mm, at least about 200 mm, at least about 300 mm, or at leastabout 450 mm. Wafer thicknesses may vary from about 250 micrometers toabout 1500 micrometers, such as between about 300 micrometers and about1000 micrometers, suitably within the range of about 500 micrometers toabout 1000 micrometers. In some specific embodiments, the waferthickness may be about 725 micrometers.

In particularly preferred embodiments, the single crystal semiconductorwafers comprise single crystal silicon wafers which have been slicedfrom a single crystal ingot grown in accordance with conventionalCzochralski crystal growing methods or float zone growing methods. Suchmethods, as well as standard silicon slicing, lapping, etching, andpolishing techniques are disclosed, for example, in F. Shimura,Semiconductor Silicon Crystal Technology, Academic Press, 1989, andSilicon Chemical Etching, (J. Grabmaier ed.) Springer-Verlag, N.Y., 1982(incorporated herein by reference). Preferably, the wafers are polishedand cleaned by standard methods known to those skilled in the art. See,for example, W.C. O'Mara et al., Handbook of Semiconductor SiliconTechnology, Noyes Publications. If desired, the wafers can be cleaned,for example, in a standard SC1/SC2 solution. In some embodiments, thesingle crystal silicon wafers of the present invention are singlecrystal silicon wafers which have been sliced from a single crystalingot grown in accordance with conventional Czochralski (“Cz”) crystalgrowing methods, typically having a nominal diameter of at least about150 mm, at least about 200 mm, at least about 300 mm, or at least about450 mm. Preferably, both the single crystal silicon handle wafer and thesingle crystal silicon donor wafer have mirror-polished front surfacefinishes that are free from surface defects, such as scratches, largeparticles, etc. Wafer thickness may vary from about 250 micrometers toabout 1500 micrometers, such as between about 300 micrometers and about1000 micrometers, suitably within the range of about 500 micrometers toabout 1000 micrometers. In some specific embodiments, the waferthickness may be about 725 micrometers.

In some embodiments, the single crystal semiconductor handle substrateand the single crystal semiconductor donor substrate, i.e., singlecrystal semiconductor handle wafer and single crystal semiconductordonor wafer, comprise interstitial oxygen in concentrations that aregenerally achieved by the Czochralski-growth method. In someembodiments, the semiconductor wafers comprise oxygen in a concentrationbetween about 4 PPMA and about 18 PPMA. In some embodiments, thesemiconductor wafers comprise oxygen in a concentration between about 10PPMA and about 35 PPMA. Preferably, the single crystal silicon handlewafer comprises oxygen in a concentration of no greater than about 10PPMA. Interstitial oxygen may be measured according to SEMI MF1188-1105.

In some embodiments, the semiconductor handle substrate, e.g., a singlecrystal semiconductor handle substrate, such as a single crystal siliconhandle wafer, has a relatively high minimum bulk resistivity. Highresistivity wafers are generally sliced from single crystal ingots grownby the Czochralski method or float zone method. Cz-grown silicon wafersmay be subjected to a thermal anneal at a temperature ranging from about600° C. to about 1000° C. in order to annihilate thermal donors causedby oxygen that are incorporated during crystal growth. In someembodiments, the single crystal semiconductor handle wafer has a minimumbulk resistivity of at least 100 Ohm-cm, at least about 500 Ohm-cm, atleast about 1000 Ohm-cm, or even at least about 3000 Ohm-cm, such asbetween about 100 Ohm-cm and about 100,000 Ohm-cm, or between about 500Ohm-cm and about 100,000 Ohm-cm, or between about 1000 Ohm-cm and about100,000 Ohm-cm, or between about 500 Ohm-cm and about 10,000 Ohm-cm, orbetween about 750 Ohm-cm and about 10,000 Ohm-cm, between about 1000Ohm-cm and about 10,000 Ohm-cm, between about 2000 Ohm-cm and about10,000 Ohm-cm, between about 3000 Ohm-cm and about 10,000 Ohm-cm, orbetween about 3000 Ohm-cm and about 5,000 Ohm-cm. Methods for preparinghigh resistivity wafers are known in the art, and such high resistivitywafers may be obtained from commercial suppliers, such as SunEdisonSemiconductor Ltd. (St. Peters, Mo.; formerly MEMC Electronic Materials,Inc.).

In some embodiments, the single crystal semiconductor handle wafersurface could be intentionally damaged by a sound blasting process or bya caustic etch.

In some embodiments, the front surface of the semiconductor handle waferis treated to form an interfacial layer prior to formation of the chargetrapping layer. The interfacial layer may comprise a material selectedfrom silicon dioxide, silicon nitride, and silicon oxynitride. In somepreferred embodiments, the interfacial layer may comprise silicondioxide. In order to form a silicon dioxide interfacial layer, the frontsurface of the semiconductor handle wafer is oxidized prior to formationof the charge trapping layer such that the front surface of the wafercomprises an oxide film. In some embodiments, the interfacial layercomprises silicon dioxide, which may be formed by oxidizing the frontsurface of the semiconductor handle substrate. This may be accomplishedby means known in the art, such as thermal oxidation (in which someportion of the deposited semiconductor material film will be consumed)or CVD oxide deposition. In some embodiments, the single crystalsemiconductor handle substrate, e.g., a single crystal silicon handlewafer, may be thermally oxidized in a furnace such as an ASM A400. Thetemperature may range from 750° C. to 1200° C. in an oxidizing ambient.The oxidizing ambient atmosphere can be a mixture of inert gas, such asAr or N₂, and O₂. The oxygen content may vary from 1 to 10 percent, orhigher. In some embodiments, the oxidizing ambient atmosphere may be upto 100% (a “dry oxidation”). In an exemplary embodiment, semiconductorhandle wafers may be loaded into a vertical furnace, such as an A400.The temperature is ramped to the oxidizing temperature with a mixture ofN₂ and O₂. After the desired oxide thickness has been obtained, the O₂is turned off and the furnace temperature is reduced and wafers areunloaded from the furnace. In order to incorporate nitrogen in theinterfacial layer to deposit silicon nitride or silicon oxynitride, theatmosphere may comprise nitrogen alone or a combination of oxygen andnitrogen, and the temperature may be increased to a temperature between1100° C. and 1400° C. An alternative nitrogen source is ammonia. In someembodiments, the handle substrates are oxidized to provide an oxidelayer of at least about 7 angstroms thick, such as between about 7angstroms and about 20 angstroms, or between about 10 angstroms andabout 20 angstroms.

According to the method of the present invention, semiconductor materialis deposited onto the exposed front surface of the single crystalsemiconductor handle wafer, which preferably comprises an exposedoxidized front surface layer. Semiconductor material suitable for use informing a charge trapping layer in a semiconductor-on-insulator deviceis suitably capable of forming a highly defective layer in thefabricated device. Such materials include polycrystalline semiconductormaterials and amorphous semiconductor materials. Materials that may bepolycrystalline or amorphous include silicon (Si), silicon germanium(SiGe), silicon doped with carbon (SiC), and germanium (Ge).Polycrystalline silicon denotes a material comprising small siliconcrystals having random crystal orientations. Polycrystalline silicongrains may be as small in size as about 20 nanometers. According to themethod of the present invention, the smaller the crystal grain size ofpolycrystalline silicon deposited the higher the defectivity in thecharge trapping layer. Amorphous silicon comprises a non-crystallineallotropic form of silicon, which lacks short range and long rangeorder. Silicon grains having crystallinity over no more than about 10nanometers may also be considered essentially amorphous. Silicongermanium comprises an alloy of silicon germanium in any molar ratio ofsilicon and germanium. Silicon doped with carbon comprises a compound ofsilicon and carbon, which may vary in molar ratio of silicon and carbon.Preferably, the charge trapping layer has a resistivity at least about1000 Ohm-cm, or at least about 3000 Ohm-cm, such as between about 1000Ohm-cm and about 100,000 Ohm-cm, between about 1000 Ohm-cm and about10,000 Ohm-cm, between about 2000 Ohm-cm and about 10,000 Ohm-cm,between about 3000 Ohm-cm and about 10,000 Ohm-cm, or between about 3000Ohm-cm and about 5,000 Ohm-cm.

The material for deposition onto the, optionally oxidized, front surfaceof the single crystal semiconductor handle wafer may be deposited bymeans known in the art. For example, the semiconductor material may bedeposited using metalorganic chemical vapor deposition (MOCVD), physicalvapor deposition (PVD), chemical vapor deposition (CVD), low pressurechemical vapor deposition (LPCVD), plasma enhanced chemical vapordeposition (PECVD), or molecular beam epitaxy (MBE). Silicon precursorsfor LPCVD or PECVD include methyl silane, silicon tetrahydride (silane),trisilane, disilane, pentasilane, neopentasilane, tetrasilane,dichlorosilane (SiH₂Cl₂), silicon tetrachloride (SiCl₄), among others.For example, polycrystalline silicon may be deposited onto the surfaceoxidation layer by pyrolyzing silane (SiH₄) in a temperature rangebetween about 550° C. and about 690° C., such as between about 580° C.and about 650° C. The chamber pressure may range from about 70 to about400 mTorr. Amorphous silicon may be deposited by plasma enhancedchemical vapor deposition (PECVD) at temperatures generally rangingbetween about 75° C. and about 300° C. Silicon germanium, particularlyamorphous silicon germanium, may be deposited at temperatures up toabout 300° C. by chemical vapor deposition by including organogermaniumcompounds, such as isobutylgermane, alkylgermanium trichlorides, anddimethylaminogermanium trichloride. Silicon doped with carbon may bedeposited by thermal plasma chemical vapor deposition in epitaxialreactors using precursors such as silicon tetrachloride and methane.Suitable carbon precursors for CVD or PECVD include methylsilane,methane, ethane, ethylene, among others. For LPCVD deposition,methylsilane is a particularly preferred precursor since it providesboth carbon and silicon. For PECVD deposition, the preferred precursorsinclude silane and methane. In some embodiments, the silicon layer maycomprise a carbon concentration of at least about 1% on an atomic basis,such as between about 1% on an atomic basis and about 10% on an atomicbasis.

In some embodiments, the deposition of the semiconductor material of thecharge trap layer may be temporarily interrupted, at least once andpreferably more than once, in order to prepare multiple layers of chargetrapping material. The interim surface of the semiconductor materialfilm may be exposed to inert, oxidizing, nitridizing, or passivatingatmosphere to thereby poison or passivate the deposited semiconductormaterial. Stated another way, the method of the present invention maycomprise deposition of a multilayer of charge trapping semiconductormaterial by a cycling process in which semiconductor material isdeposited, deposition is interrupted, the layer of semiconductormaterial is poisoned or passivated, and the next layer of semiconductormaterial is deposited. In some embodiments, a multilayer may be formedcomprising one passivated semiconductor layer and one additionalsemiconductor layer may be deposited to form the charge trapping layer.In some embodiments, the multilayer comprises more than one passivatedsemiconductor layer and one additional semiconductor layer in the chargetrapping layer. By depositing the charge trapping layer in this way, amultilayer comprising, for example, one or more passivated layers, ortwo or more passivated layers, such as three or more passivated layers,such as at least four passivated layers, or between four and about 100passivated layers, or between four and about 60 passivated layers, orbetween four and about 50 passivated layers, or between four and about25 passivated layers, or between six and about 20 passivated layers ofsemiconductor material is deposited onto the handle substrate. A largenumber of semiconductor layers may be deposited limited in part bythroughput demands and by the smallest practical layer thickness thatmay be deposited, which is currently about 20 nanometers. Each of theselayers of semiconductor material is poisoned or passivated such thatduring the high temperature processes of semiconductor-on-insulatorfabrication, crystal grain growth in each layer of the multilayer islimited by the thickness of the passivated multilayer rather than by thethickness of the overall charge trapping layer as in prior artprocesses. In some embodiments, the semiconductor layers may bepassivated by exposing the first semiconductor layer to an atmospherecomprising a nitrogen-containing gas, such as nitrogen, nitrous oxide,ammonia (NH₃), nitrogen plasma, and any combination thereof. In thisregard, the atmosphere in which the semiconductor layer is deposited maycomprise a nitrogen-containing gas, such as nitrogen, and termination ofthe deposition process followed by exposure to the gas may be sufficientto form a thin passivation layer over the semiconductor layer. In someembodiments, the chamber may be evacuated of the deposition gas andpurged with the nitrogen containing gas in order to effect passivationof the previously deposited semiconductor layer. Exposure to nitrogenmay nitride the deposited semiconductor layer, for example, resulting inthe formation of a thin layer of silicon nitride of just a few angstromsthickness. Alternative passivation methods may be used. For example, thesemiconductor layer may be passivated by exposing the firstsemiconductor layer to an atmosphere comprising an oxygen containinggas, such as oxygen, ozone, water vapor, or any combination thereof.According to these embodiments, a thin layer of semiconductor oxide mayform on the semiconductor layer, the semiconductor oxide beingsufficient to passivate the layer. For example, a thin layer of siliconoxide may be formed between each layer of the multilayer. The oxidelayer may be only a few angstroms thick, such as between about 1angstrom and about 20 angstroms, or between about 1 angstrom and about10 angstroms. In some embodiments, air, which comprises both nitrogenand oxygen, may be used as the passivated gas. In some embodiments, thesemiconductor layers may be passivated by exposing the firstsemiconductor layer to a liquid selected from the group consisting ofwater, peroxide (e.g. hydrogen peroxide solution), or SCl solution(NH₃:H₂O₂:H₂O).

The overall thickness of the charge trapping layer comprising multiplepassivated semiconductor layers may be between about 0.3 micrometers andabout 5 micrometers, such as between about 0.3 micrometers and about 3micrometers, such as between about 0.3 micrometers and about 2micrometers or between about 2 micrometers and about 3 micrometers. If amultilayer approach is employed, each layer of the multilayer may be atleast about 5 nanometers thick, such as at least about 20 nanometersthick, such as between about 5 and about 1000 nanometers thick, betweenabout 20 and about 1000 nanometers thick, between about 20 and about 500nanometers thick, or between about 100 and about 500 nanometers thick.Advantageously, the passivation process imparts additional defectivityinto the charge trapping layer.

In some embodiments, the charge trapping layer comprisingpolycrystalline silicon and/or the other materials disclosed herein maybe subjected to chemical mechanical polishing (“CMP”). Chemicalmechanical polishing may occur by methods known in the art.

According to the method of the present invention, deposition of thecharge trapping layer is followed by formation of a dielectric layer onthe surface of the charge trapping layer. In some embodiments, thesingle semiconductor handle substrate (e.g., single crystal siliconhandle substrate) is oxidized to form a semiconductor oxide (e.g., asilicon dioxide) film on the charge trapping layer. In some embodiments,the charge trapping layer, e.g., polycrystalline film, may be thermallyoxidized (in which some portion of the deposited semiconductor materialfilm will be consumed) or the semiconductor oxide (e.g., silicondioxide) film may be grown by CVD oxide deposition. The nature of thesemiconductor oxide depends in part on the components of the chargetrapping layer. That is, charge trapping layers comprisingpolycrystalline or amorphous silicon may be oxidized to form silicondioxide films. The charge trapping layer may additionally oralternatively comprise silicon germanium (SiGe), silicon doped withcarbon (SiC), and germanium (Ge), which would yield semiconductor oxidelayers comprising oxides of SiGe, SiC, and/or Ge. In some embodiments,the single crystal semiconductor handle substrate comprising the chargetrapping layer may be thermally oxidized in a furnace such as an ASMA400. The temperature may range from 750° C. to 1200° C. in an oxidizingambient. The oxidizing ambient atmosphere can be a mixture of inert gas,such as Ar or N₂, and O₂. The oxygen content may vary from 1 to 10percent, or higher. In some embodiments, the oxidizing ambientatmosphere may be up to 100% (a “dry oxidation”). In an exemplaryembodiment, semiconductor handle wafers comprising the charge trappinglayer may be loaded into a vertical furnace, such as an A400. Thetemperature is ramped to the oxidizing temperature with a mixture of N₂and O₂. After the desired oxide thickness has been obtained, the O₂ isturned off and the furnace temperature is reduced and wafers areunloaded from the furnace. In order to incorporate nitrogen in theinterfacial layer to deposit silicon nitride or silicon oxynitride, theatmosphere may comprise nitrogen alone or a combination of oxygen andnitrogen, and the temperature may be increased to a temperature between1100° C. and 1400° C. An alternative nitrogen source is ammonia. Theoxide layer (e.g., silicon dioxide layer) in contact with thepolycrystalline or amorphous charge trapping layer (e.g., apolycrystalline or amorphous silicon charge trapping layer) may have athickness between about 0.1 micrometer and about 10 micrometers, such asbetween about 0.1 micrometers and about 4 micrometers, such as betweenabout 0.1 micrometers and about 2 micrometers, or between about 0.1micrometers and about 1 micrometer. The oxidation process additionallyoxidizes the back surface of the single crystal semiconductor handlewafer, which advantageously reduces warp and bow potentially caused bythe different coefficients of thermal expansion of silicon and silicondioxide.

After oxidation of the charge trapping layer, wafer cleaning isoptional. If desired, the wafers can be cleaned, for example, in astandard SC1/SC2 solution. Additionally, the wafers, particularly, thesilicon dioxide layer on the charge trapping layer, may be subjected tochemical mechanical polishing (CMP) to reduce the surface roughness,preferably to the level of RMS_(2×2 μm2) less than about 5 angstroms,wherein root mean squared

${R_{q} = \sqrt{\frac{1}{n}{\sum\limits_{i = 1}^{n}y_{i}^{2}}}},$

the roughness profile contains ordered, equally spaced points along thetrace, and y_(i) is the vertical distance from the mean line to the datapoint.

The single crystal semiconductor handle wafer prepared according to themethod described herein to comprise a charge trapping layer (e.g.,polycrystalline or amorphous silicon) and a semiconductor oxide (e.g., asilicon dioxide) film having a thickness of at least about 0.1micrometers, is next bonded a single crystal semiconductor donorsubstrate, e.g., a single crystal semiconductor donor wafer, which isprepared according to conventional layer transfer methods. The singlecrystal semiconductor donor substrate may be a single crystalsemiconductor wafer. In preferred embodiments, the semiconductor wafercomprises a semiconductor material selected from the group consisting ofsilicon, silicon carbide, silicon germanium, gallium arsenide, galliumnitride, indium phosphide, indium gallium arsenide, germanium, andcombinations thereof. Depending upon the desired properties of the finalintegrated circuit device, the single crystal semiconductor (e.g.,silicon) donor wafer may comprise a dopant selected from the groupconsisting of boron, arsenic, and phosphorus. The resistivity of thesingle crystal semiconductor (e.g., silicon) donor wafer may range from1 to 50 Ohm-cm, typically, from 5 to 25 Ohm-cm. The single crystalsemiconductor donor wafer may be subjected to standard process stepsincluding oxidation, implant, and post implant cleaning. Accordingly, asemiconductor donor substrate, such as a single crystal semiconductorwafer of a material that is conventionally used in preparation ofmultilayer semiconductor structures, e.g., a single crystal silicondonor wafer, that has been etched and polished and optionally oxidized,is subjected to ion implantation to form a damage layer in the donorsubstrate.

In some embodiments, the semiconductor donor substrate comprises adielectric layer. Suitable dielectric layers may comprise a materialselected from among silicon dioxide, silicon nitride, hafnium oxide,titanium oxide, zirconium oxide, lanthanum oxide, barium oxide, and acombination thereof. In some embodiments, the dielectric layer comprisesan oxide layer having a thickness of at least about 10 nanometer thick,such as between about 10 nanometers and about 10,000 nanometers, betweenabout 10 nanometers and about 5,000 nanometers, or between about 100nanometers and about 800 nanometers, such as about 600 nanometers.

In some embodiments, the front surface of the single crystalsemiconductor donor substrate (e.g., a single crystal silicon donorsubstrate) may be thermally oxidized (in which some portion of thedeposited semiconductor material film will be consumed) to prepare thesemiconductor oxide film, or the semiconductor oxide (e.g., silicondioxide) film may be grown by CVD oxide deposition. In some embodiments,the front surface of the single crystal semiconductor donor substratemay be thermally oxidized in a furnace such as an ASM A400 in the samemanner described above. In some embodiments, the donor substrates areoxidized to provide an oxide layer on the front surface layer of atleast about 10 nanometer thick, such as between about 10 nanometers andabout 10,000 nanometers, between about 10 nanometers and about 5,000nanometers, or between about 100 nanometers and about 800 nanometers,such as about 600 nanometers.

Ion implantation may be carried out in a commercially availableinstrument, such as an Applied Materials Quantum II. Implanted ionsinclude He, H, H₂, or combinations thereof. Ion implantation is carriedout as a density and duration sufficient to form a damage layer in thesemiconductor donor substrate. Implant density may range from about 10¹²ions/cm² to about 10¹⁷ ions/cm², such as from about 10¹⁴ ions/cm² toabout 10¹⁷ ions/cm². Implant energies may range from about 1 keV toabout 3,000 keV, such as from about 10 keV to about 3,000 keV. The depthof implantation determines the thickness of the single crystalsemiconductor device layer in the final SOI structure. In someembodiments it may be desirable to subject the single crystalsemiconductor donor wafers, e.g., single crystal silicon donor wafers,to a clean after the implant. In some preferred embodiments, the cleancould include a Piranha clean followed by a DI water rinse and SC1/SC2cleans.

In some embodiments of the present invention, the single crystalsemiconductor donor substrate having an ion implant region thereinformed by helium ion and/or hydrogen ion implant is annealed at atemperature sufficient to form a thermally activated cleave plane in thesingle crystal semiconductor donor substrate. An example of a suitabletool might be a simple Box furnace, such as a Blue M model. In somepreferred embodiments, the ion implanted single crystal semiconductordonor substrate is annealed at a temperature of from about 200° C. toabout 350° C., from about 225° C. to about 325° C., preferably about300° C. Thermal annealing may occur for a duration of from about 2 hoursto about 10 hours, such as from about 2 hours to about 8 hours. Thermalannealing within these temperatures ranges is sufficient to form athermally activated cleave plane. After the thermal anneal to activatethe cleave plane, the single crystal semiconductor donor substratesurface is preferably cleaned.

In some embodiments, the ion-implanted and optionally cleaned andoptionally annealed single crystal semiconductor donor substrate issubjected to oxygen plasma and/or nitrogen plasma surface activation. Insome embodiments, the oxygen plasma surface activation tool is acommercially available tool, such as those available from EV Group, suchas EVG®810LT Low Temp Plasma Activation System. The ion-implanted andoptionally cleaned single crystal semiconductor donor wafer is loadedinto the chamber. The chamber is evacuated and backfilled with O₂ to apressure less than atmospheric to thereby create the plasma. The singlecrystal semiconductor donor wafer is exposed to this plasma for thedesired time, which may range from about 1 second to about 120 seconds.Oxygen plasma surface oxidation is performed in order to render thefront surface of the single crystal semiconductor donor substratehydrophilic and amenable to bonding to a single crystal semiconductorhandle substrate prepared according to the method described above.

The hydrophilic front surface layer of the single crystal semiconductordonor substrate and the front surface of the single crystalsemiconductor handle substrate, which is optionally oxidized, are nextbrought into intimate contact to thereby form a bonded structure. Thebonded structure comprises a dielectric layer, e.g., a buried oxide,with a portion of the dielectric layer contributed by the oxidized frontsurface of the single crystal semiconductor handle substrate and aportion of the dielectric layer contributed by the oxidized frontsurface of the single crystal semiconductor donor substrate. In someembodiments, the dielectric layer, e.g., buried oxide layer, has athickness of at least about 10 nanometer thick, such as between about 10nanometers and about 10,000 nanometers, between about 10 nanometers andabout 5,000 nanometers, or between about 100 nanometers and about 800nanometers, such as about 600 nanometers.

Since the mechanical bond is relatively weak, the bonded structure isfurther annealed to solidify the bond between the donor wafer and thehandle wafer. In some embodiments of the present invention, the bondedstructure is annealed at a temperature sufficient to form a thermallyactivated cleave plane in the single crystal semiconductor donorsubstrate. An example of a suitable tool might be a simple Box furnace,such as a Blue M model. In some preferred embodiments, the bondedstructure is annealed at a temperature of from about 200° C. to about350° C., from about 225° C. to about 325° C., preferably about 300° C.Thermal annealing may occur for a duration of from about 0.5 hours toabout 10 hour, preferably a duration of about 2 hours. Thermal annealingwithin these temperatures ranges is sufficient to form a thermallyactivated cleave plane. After the thermal anneal to activate the cleaveplane, the bonded structure may be cleaved.

After the thermal anneal, the bond between the single crystalsemiconductor donor substrate and the single crystal semiconductorhandle substrate is strong enough to initiate layer transfer viacleaving the bonded structure at the cleave plane. Cleaving may occuraccording to techniques known in the art. In some embodiments, thebonded structure may be placed in a conventional cleave station affixedto stationary suction cups on one side and affixed by additional suctioncups on a hinged arm on the other side. A crack is initiated near thesuction cup attachment and the movable arm pivots about the hingecleaving the wafer apart. Cleaving removes a portion of thesemiconductor donor wafer, thereby leaving a semiconductor device layer,preferably a silicon device layer, on the semiconductor-on-insulatorcomposite structure.

After cleaving, the cleaved structure may be subjected to a hightemperature anneal in order to further strengthen the bond between thetransferred device layer and the single crystal semiconductor handlesubstrate. An example of a suitable tool might be a vertical furnace,such as an ASM A400. In some preferred embodiments, the bonded structureis annealed at a temperature of from about 1000° C. to about 1200° C.,preferably at about 1000° C. Thermal annealing may occur for a durationof from about 0.5 hours to about 8 hours, preferably a duration of about4 hours. Thermal annealing within these temperatures ranges issufficient to strengthen the bond between the transferred device layerand the single crystal semiconductor handle substrate.

After the cleave and high temperature anneal, the bonded structure maybe subjected to a cleaning process designed to remove thin thermal oxideand clean particulates from the surface. In some embodiments, the singlecrystal semiconductor donor wafer may be brought to the desiredthickness and smoothness by subjecting to a vapor phase HCl etch processin a horizontal flow single wafer epitaxial reactor using H₂ as acarrier gas. In some embodiments, an epitaxial layer may be deposited onthe transferred device layer. With reference to FIG. 3, the finishedmultilayer structure 100 of the invention, i.e., a SOI wafer, comprisesthe high resistivity single crystal semiconductor handle substrate 102(e.g., a single crystal silicon handle substrate), a charge trappinglayer 104, a semiconductor oxide 108 (e.g., silicon dioxide layer)prepared from oxidation of the charge trapping layer 104, a dielectriclayer 110 (e.g., buried oxide layer) prepared from oxidation of thesingle crystal semiconductor donor substrate, and the semiconductordevice layer 106 (prepared by thinning the donor substrate). The bondingsurface 112 is shown between the first oxide layer 108 and the secondoxide layer 110. Oxidation further forms the backside oxide layer 116,which is advantageous for reducing wafer bow. The final structure maythen be subjected to end of line metrology inspections and cleaned afinal time using typical SC1-SC2 process.

Having described the invention in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims.

The following non-limiting examples further illustrate the presentinvention.

EXAMPLE 1

A multilayer structure 100 of the invention is illustrated in FIG. 3.The multilayer structure 100 comprises a high resistivity siliconsubstrate 102 having a backside oxide layer 116, a charge trapping layer104, and a silicon device layer 106. Two oxide layers 108, 110 liebetween the charge trapping layer 104 and the silicon device layer 106.The first oxide layer 108 is grown by thermal oxidation of the chargetrapping layer 104. The second oxide layer 110 is grown by CVD oxidationof the silicon donor wafer in a chemical vapor deposition (CVD) system.The bonding surface 112 is shown between the first oxide layer 108 andthe second oxide layer 110. The removed portion of the donor wafer 114is shown for reference. The multilayer structure 100 of the Example wasprepared according to the following protocol.

200 mm single side polished high resistivity single crystal siliconwafer substrate 102 with resistivity >500 Ohm-cm, or >1000 Ohm-cm,or >3000 Ohm-cm (SunEdison, Inc.; St. Peters, Mo.) was provided. Acharge trapping layer 104 comprising polycrystalline silicon wasdeposited on the front surface of the single crystal silicon handlewafer 102. The charge trapping layer 104 was deposited in LPCVD reactorin a temperature range between 550 and 690° C. and tube pressure rangingfrom 70 to 400 mTorr. A preferred LPCVD reactor is a vertical reactorwith three injection points, but the same result could also be reachedin other vertical reactors or horizontal furnaces. The charge trappinglayer 104 was optionally chemical mechanical polished. Next, thepolycrystalline silicon charge trapping layer 104 was subjected tothermal oxidation to form the first oxide layer 108 to an oxidethickness to >0.1 μm. Oxidation further forms the backside oxide layer116, which is advantageous for reducing wafer bow. The first oxide layer108 was chemical-mechanical polished to achieve the level of itsroughness RMS_(2×2 μm2)<5A. The single crystal silicon wafer substrate102 comprising the charge trapping layer 104 and the first oxide layer108 is next bonded to a donor wafer 114 comprising a second oxide layer110. Before bonding, the donor wafers receive oxidation; implantationwith He⁺ and H⁺ (or H2⁺) ions; and anneal. The donor wafers 114 aremechanically cleaved leaving a thin top silicon layer 106 on the surfaceof handle substrate 102 with the deposited semiconductor material CTL104 underneath of first oxide layer 108 and second oxide layer 110,which becomes BOX. Optionally, the top silicon layer is thinned to adesired thickness; the top silicon layer may be smoothed to meet SOIsurface roughness requirement; and optionally, an epitaxial layer isgrown on the top SOI.

As various changes could be made in the above compositions and processeswithout departing from the scope of the invention, it is intended thatall matter contained in the above description be interpreted asillustrative and not in a limiting sense.

When introducing elements of the present invention or the preferredembodiment(s) thereof, the articles “a,” “an,” “the,” and “said” areintended to mean that there are one or more of the elements. The terms“comprising,” “including,” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

What is claimed is:
 1. A method of preparing a semiconductor-on-insulator device, the method comprising: forming a charge trapping layer on a front surface layer of a single crystal semiconductor handle substrate, wherein the single crystal semiconductor handle substrate comprises two major, generally parallel surfaces, one of which is the front surface of the single crystal semiconductor handle substrate and the other of which is a back surface of the single crystal semiconductor handle substrate, a circumferential edge joining the front and back surfaces of the single crystal semiconductor handle substrate, a bulk region between the front and back surfaces, and a central plane of the single crystal semiconductor handle substrate between the front and back surfaces of the single crystal semiconductor handle substrate, wherein the single crystal semiconductor handle substrate has a minimum bulk region resistivity of 100 Ohm-cm and further wherein the charge trapping layer comprises one or more semiconductor layers, wherein each of the one or more semiconductor layers comprise a polycrystalline structure or an amorphous structure and further wherein each of the one or more semiconductor layers comprises a material selected from the group consisting of silicon, SiGe, SiC, and Ge; forming a semiconductor oxide layer on the charge trapping layer, wherein the semiconductor oxide layer has a thickness of at least about 0.1 micrometers; and bonding the semiconductor oxide layer to a dielectric layer on a front surface layer of a single crystal semiconductor donor substrate to thereby prepare a bonded structure, wherein the single crystal semiconductor donor substrate comprises two major, generally parallel surfaces, one of which is the front surface of the single crystal semiconductor donor substrate and the other of which is a back surface of the single crystal semiconductor donor substrate, a circumferential edge joining the front and back surfaces of the single crystal semiconductor donor substrate, and a central plane of the single crystal semiconductor donor substrate between the front and back surfaces of the single crystal semiconductor donor substrate, wherein the single crystal semiconductor donor substrate comprises a cleave plane and the dielectric layer on the front surface layer of the single crystal semiconductor donor substrate.
 2. The method of claim 1 wherein the single crystal semiconductor handle substrate comprises a semiconductor material selected from the group consisting of silicon, silicon carbide, silicon germanium, gallium arsenide, gallium nitride, indium phosphide, indium gallium arsenide, germanium, and combinations thereof.
 3. The method of claim 1 wherein the single crystal semiconductor handle substrate comprises a single crystal silicon wafer sliced from a single crystal silicon ingot grown by the Czochralski method or the float zone method.
 4. The method of claim 1 wherein the single crystal semiconductor handle substrate has a bulk resistivity between about 100 Ohm-cm and about 100,000 Ohm-cm.
 5. The method of claim 1 wherein the single crystal semiconductor handle substrate has a bulk resistivity between about 2000 Ohm-cm and about 10,000 Ohm-cm.
 6. The method of claim 1 wherein the single crystal semiconductor handle substrate has a bulk resistivity between about 3000 Ohm-cm and about 5,000 Ohm-cm.
 7. The method of claim 1 wherein the charge trapping layer has a resistivity greater than about 1000 Ohm-cm.
 8. The method of claim 1 wherein the charge trapping layer has a resistivity greater than about 3000 Ohm-cm.
 9. The method of claim 1 wherein the charge trapping layer has a resistivity between about 2000 Ohm-cm and about 10,000 Ohm-cm.
 10. The method of claim 1 wherein the charge trapping layer has a resistivity between about 3000 Ohm-cm and about 10,000 Ohm-cm.
 11. The method of claim 1 wherein the charge trapping layer has a resistivity between about 3000 Ohm-cm and about 5,000 Ohm-cm.
 12. The method of claim 1 wherein the total thickness of the charge trapping layer is between about 0.3 micrometers and about 5 micrometers.
 13. The method of claim 1 wherein the total thickness of the charge trapping layer is between about 0.3 micrometers and about 2 micrometers.
 14. The method of claim 1 wherein the charge trapping layer comprises two or more semiconductor layers, wherein each of the two or more semiconductor layers are passivated.
 15. The method of claim 1 wherein the charge trapping layer comprises SiGe, as a polycrystalline structure or an amorphous structure.
 16. The method of claim 1 wherein the charge trapping layer comprises SiC, as a polycrystalline structure or an amorphous structure.
 17. The method of claim 1 wherein the charge trapping layer comprises Ge, as a polycrystalline structure or an amorphous structure.
 18. The method of claim 1 wherein semiconductor oxide layer in interfacial contact with the charge trapping layer has a thickness of at least about 0.1 micrometer.
 19. The method of claim 1 wherein semiconductor oxide layer in interfacial contact with the charge trapping layer has a thickness between about 0.1 micrometer and about 10 micrometers.
 20. The method of claim 1 wherein semiconductor oxide layer in interfacial contact with the charge trapping layer has a thickness between about 0.1 micrometer and about 2 micrometers.
 21. The method of claim 1 wherein the dielectric layer has a thickness between about 10 nanometers and about 10,000 nanometers.
 22. The method of claim 1 wherein the single crystal semiconductor donor substrate comprises a semiconductor material selected from the group consisting of silicon, silicon carbide, silicon germanium, gallium arsenide, gallium nitride, indium phosphide, indium gallium arsenide, germanium, and combinations thereof.
 23. The method of claim 1 wherein the single crystal semiconductor donor substrate has a resistivity between about 1 and about 50 Ohm-cm.
 24. The method of claim 1 further comprising heating the bonded structure at a temperature and for a duration sufficient to strengthen the bond between the dielectric layer of the single crystal semiconductor donor structure and the semiconductor oxide on the front surface of the single crystal semiconductor handle substrate.
 25. The method of claim 1 further comprising: mechanically cleaving the bonded structure at the cleave plane of the single crystal semiconductor donor substrate to thereby prepare the semiconductor-on-insulator device comprising the single crystal semiconductor handle substrate, the charge trapping layer, semiconductor oxide layer, the dielectric layer in contact with the semiconductor oxide layer, and a single crystal semiconductor device layer in contact with the dielectric layer; and heating the cleaved structure at a temperature and for a duration sufficient to strengthen the bond.
 26. A method of preparing a silicon-on-insulator structure, the method comprising: bonding a first bonding surface on a front surface layer of a single crystal silicon handle substrate to a second bonding surface on a front surface layer of a single crystal silicon donor substrate; wherein the single crystal silicon handle substrate comprises two major, generally parallel surfaces, one of which is the front surface of the single crystal silicon handle substrate and the other of which is a back surface of the single crystal silicon handle substrate, a circumferential edge joining the front and back surfaces of the single crystal silicon handle substrate, a bulk region between the front and back surfaces, and a central plane of the single crystal silicon handle substrate between the front and back surfaces of the single crystal silicon handle substrate, wherein the single crystal silicon handle substrate has a minimum bulk region resistivity of 100 Ohm-cm, and further wherein a charge trapping layer is in interfacial contact with the front surface layer of the single crystal silicon handle substrate, the charge trapping layer comprising one or more semiconductor layers, wherein each of the one or more semiconductor layers comprise a polycrystalline structure or an amorphous structure and further wherein each of the one or more semiconductor layers comprises a material selected from the group consisting of silicon, SiGe, SiC, and Ge, and further wherein a semiconductor oxide layer is in interfacial contact with the charge trapping layer, the semiconductor oxide layer comprising the first bonding surface; and wherein the single crystal silicon donor substrate comprises two major, generally parallel surfaces, one of which is the front surface of the single crystal silicon donor substrate and the other of which is a back surface of the single crystal silicon donor substrate, a circumferential edge joining the front and back surfaces of the single crystal silicon donor substrate, and a central plane of the single crystal silicon donor substrate between the front and back surfaces of the single crystal silicon donor substrate, wherein the single crystal silicon donor substrate comprises a cleave plane and a dielectric layer on the front surface layer of the single crystal silicon donor substrate, the dielectric layer comprising the second bonding surface.
 27. The method of claim 26 wherein the single crystal silicon handle substrate comprises a single crystal silicon wafer sliced from a single crystal silicon ingot grown by the Czochralski method or the float zone method.
 28. The method of claim 26 wherein the single crystal silicon handle substrate has a bulk resistivity between about 100 Ohm-cm and about 100,000 Ohm-cm.
 29. The method of claim 26 wherein the single crystal silicon handle substrate has a bulk resistivity between about 1000 Ohm-cm and about 10,000 Ohm-cm.
 30. The method of claim 26 wherein the charge trapping layer has a resistivity greater than about 1000 Ohm-cm.
 31. The method of claim 26 wherein the charge trapping layer has a resistivity greater than about 3000 Ohm-cm.
 32. The method of claim 26 wherein the charge trapping layer has a resistivity between about 2000 Ohm-cm and about 10,000 Ohm-cm.
 33. The method of claim 26 wherein the charge trapping layer has a resistivity between about 3000 Ohm-cm and about 10,000 Ohm-cm.
 34. The method of claim 26 wherein the charge trapping layer has a resistivity between about 3000 Ohm-cm and about 5,000 Ohm-cm.
 35. The method of claim 26 wherein the total thickness of the charge trapping layer is between about 0.3 micrometers and about 5 micrometers.
 36. The method of claim 26 wherein the total thickness of the charge trapping layer is between about 0.3 micrometers and about 2 micrometers.
 37. The method of claim 26 wherein the charge trapping layer comprises two or more semiconductor layers, wherein each of the two or more semiconductor layers are passivated.
 38. The method of claim 26 wherein the charge trapping layer comprises SiGe, as a polycrystalline structure or an amorphous structure.
 39. The method of claim 26 wherein the charge trapping layer comprises SiC, as a polycrystalline structure or an amorphous structure.
 40. The method of claim 26 wherein the charge trapping layer comprises Ge, as a polycrystalline structure or an amorphous structure.
 41. The method of claim 26 wherein semiconductor oxide layer in interfacial contact with the charge trapping layer has a thickness of at least about 0.1 micrometer.
 42. The method of claim 26 wherein semiconductor oxide layer in interfacial contact with the charge trapping layer has a thickness between about 0.1 micrometer and about 10 micrometers.
 43. The method of claim 26 wherein semiconductor oxide layer in interfacial contact with the charge trapping layer has a thickness between about 0.1 micrometer and about 2 micrometers.
 44. The method of claim 26 wherein the dielectric layer has a thickness between about 10 nanometers and about 10,000 nanometers.
 45. The method of claim 26 wherein the single crystal silicon donor substrate is sliced from a single crystal silicon ingot grown by the Czochralski method or the float zone method.
 46. The method of claim 26 wherein the single crystal silicon donor substrate has a resistivity between about 1 and about 50 Ohm-cm.
 47. The method of claim 26 wherein the single crystal silicon donor substrate has a resistivity between about 5 and about 25 Ohm-cm.
 48. The method of claim 26 further comprising: heating the bonded structure at a temperature and for a duration sufficient to strengthen the bond between the dielectric layer of the single crystal silicon donor structure and the semiconductor oxide on the front surface of the single crystal silicon handle substrate; mechanically cleaving the bonded structure at the cleave plane of the single crystal silicon donor substrate to thereby prepare the silicon-on-insulator device comprising the single crystal silicon handle substrate, the charge trapping layer, semiconductor oxide layer, the dielectric layer in contact with the semiconductor oxide layer, and a single crystal silicon device layer in contact with the dielectric layer; and heating the cleaved structure at a temperature and for a duration sufficient to strengthen the bond. 